Function std::ptr::write_bytes

pub unsafe extern "rust-intrinsic" fn write_bytes<T>(
    dst: *mut T, 
    val: u8, 
    count: usize
)

Sets count * size_of::<T>() bytes of memory starting at dst to val.

write_bytes is semantically equivalent to C's memset.

Safety

Behavior is undefined if any of the following conditions are violated:

• The region of memory which begins at dst and has a length of count bytes must be valid.

• dst must be properly aligned.

Additionally, the caller must ensure that writing count bytes to the given region of memory results in a valid value of T. Creating an invalid value of T can result in undefined behavior. An example is provided below.

Examples

Basic usage:

use std::ptr;

let mut vec = vec![0; 4];
unsafe {
    let vec_ptr = vec.as_mut_ptr();
    ptr::write_bytes(vec_ptr, b'a', 2);
}
assert_eq!(vec, [b'a', b'a', 0, 0]);

Creating an invalid value:

use std::{mem, ptr};

let mut v = Box::new(0i32);

unsafe {
    // Leaks the previously held value by overwriting the `Box<T>` with
    // a null pointer.
    ptr::write_bytes(&mut v, 0, mem::size_of::<Box<i32>>());
}

// At this point, using or dropping `v` results in undefined behavior.
// v = Box::new(0i32); // ERROR